Multiphase BiVO4 for environmental applications

Abstract

The synthesis of BiVO₄ multiphase photocatalysts was approached using a method and conditions designed to produce tetragonal-rich and monoclinic-rich materials with varying morphologies. The results of the SEM analysis indicated that a pH range of 3 to 7 during the hydrothermal process facilitates the formation of spherical particles with a diameter of 3.3–3.4 μm, comprising 6–7 nm crystals. Conversely, a pH value below 3 or the addition of CTAB as a surfactant resulted in the crystallization of nanocrystals with a size range of 0.5–5.0 μm, exhibiting well-defined facets. X-ray diffraction (XRD) analysis demonstrated that the former are predominantly tetragonal in variety, with a minor component of monoclinic. In the case of the latter, XRD in conjunction with electronic property analysis enabled the detection of the tetragonal variety in quantities below the detection threshold of the XRD, accompanied by the monoclinic variety. The monoclinic-rich BiVO₄ exhibited notable discrepancies in its electrokinetic parameters, including hydrothermal diameter, in comparison to the tetragonal-rich samples. Moreover, PL studies revealed that the monoclinic-rich samples exhibited up to a 100-fold reduction in emissions, with a decay time up to six times longer which is attributed to the presence of point defects. Monoclinic-rich samples also demonstrate enhanced activity with regard to the degradation of Rhodamine B and basic Fuchsin. In particular, the former exhibits superior performance, achieving results that are several times more effective. Radical scavenging tests showed that ^•OH radicals were responsible for degrading bF and RhB dyes. The enhanced photocatalytic properties of monoclinic-rich samples were ascribed to augmented absorption, restricted recombination of charge carriers, and the existence of point defects.